Water-in-oil emulsions (oil-mud) are often used in circulating fluids required in the rotary drilling of formations containing hydrocarbons. These circulating fluids are referred to as drilling muds. These oil-mud circulating fluids are pumped down the drill pipe and out into the wellbore through holes in the drill bit and back up the well in the annular space between the drill pipe and walls of the wellbore, carrying with it drill cuttings and the like that are then removed before recirculation. This mud performs a number of functions, including removing drill cuttings, lubricating and keeping the bit cool, providing flotation to help support the weight of the drill pipe and casing, coating the wellbore surface to prevent caving in and undesirable flow of fluids in or out of the wellbore, including drilling fluids, brine, and the like.
Obviously, the properties of and the composition of these drilling mud formulations are complex and variable, depending on the conditions involved and the results desired or required including reuse and recycling of mud formulations. One of the most important properties of these drilling muds and other drilling fluids is that they be thermally stable and do not present rheological and thixotropic problems under the conditions of drilling.
In these oil mud drilling fluids, the oil is the continuous phase and the water is present in a dispersed phase. This is necessary to maintain the required rheology of the mud for drilling and completion, including a balance between gel strength and viscosity, i.e., the balance for example between pumpability of the mud and its hole cleaning capability. In an oil mud, the surface of the solid materials in the mud are essentially oil wet. If, because of a number of possible factors, the solid particles begin to be water wet, handling and other problems begin. When the suspended particle surfaces become water wet and the water in oil emulsion is converted to an oil in water emulsion, which condition is referred to as "flipped", the properties of the mud are extensively affected to a degree that the mud is no longer useful. At this point, these expensive mud formulations normally have to be discarded. Usually, an oil mud in a flipped state is too thick and viscous to handle with the normal well equipment.
The undesired conversion from water in oil to oil in water emulsions includes conversion of the solid particles from an oil wet to water wet stage. This conversion or flipping can be caused by a number of factors and conditions. One source of excess water contributing to this undesirable state may come from accidental addition of water to the mud during makeup or during recycling, and cognate water introduced into the mud from formations during drilling operations. High temperature drilling conditions can cause the conversion of the water in oil to oil in water conditions. Drilled cuttings and other materials getting into the mud during drilling operations such as shale, water sensitive and water swellable clays, drilled cement, water wet solid materials, and the like can contribute to a change in the emulsion state of the oil mud. Inexpensive and incomplex techniques and methods for preventing, or more importantly, for reversing this change in emulsion state, to reverse the flipped mud, are among the objectives of this invention.